A rolling bearing unit is used to support a wheel of an automobile rotatably with respect to a suspension. Also, it is necessary to detect a rotating speed of the wheel in order to control an anti-lock brake system (ABS) or a traction control system (TCS). Because of this, in recent years, a rolling bearing unit with a rotating speed detector installed into the rolling bearing unit commonly supports the wheel rotatably with respect to the suspension and also detects the rotating speed of this wheel.
As one example of a conventional structure of the rolling bearing unit with the rotating speed detector used for such a purpose, a structure as shown in FIGS. 5 and 6 is described in Patent Document 1. A rolling bearing unit 1 with a rotating speed detector of this conventional structure rotatably supports a hub 3 which is a rotating ring in the inner side of an outer ring 2 which is a stationary ring.
The outer ring 2 in this unit 1 has double row outer ring raceways 4a, 4b on an inner peripheral surface, and a stationary side flange 5 on an outer peripheral surface, respectively. Also, in a use state, the outer ring 2 is fixed to a knuckle (not shown) constructing a suspension and is not rotated.
The hub 3 is formed by combining a hub body 6 and an inner ring 7, and has double row inner ring raceways 8a, 8b on an outer peripheral surface, and is supported in the inner side of the outer ring 2 concentrically with this outer ring 2. Concretely, the inner ring raceway 8a of the axially outboard row is directly formed on an axially intermediate portion of the outer peripheral surface of the hub body 6 and also, the inner ring 7 in which the inner ring raceway 8b of the axially inboard row is formed on the outer peripheral surface is externally fitted and fixed to a small-diameter step part 9 formed in the portion near to the axially inboard end (the inboard side in the axial direction refers to the side near to the center of an automobile body in a width direction in a state assembled to the suspension and on the other hand, the outboard side in the axial direction refers to the side near to the outside of the automobile body in the width direction, and this applies to the present description and whole claims) of the same hub body 6. And, a swaged part 10 formed by plastically deforming the axially inboard end of the hub body 6 to the radially outside direction presses an axially inboard end face of the inner ring 7. Also, the portion projected to the axially outboard side beyond an opening of the axially outboard end of the outer ring 2 in the axially outboard end of the hub body 6 is provided with a rotation side flange 11 for supporting a wheel.
Also, plural rolling elements 12, 12 are respectively formed between both of the outer ring raceways 4a, 4b and both of the inner ring raceways 8a, 8b, and the hub 3 is rotatably supported in the inner side of the outer ring 2.
Also, an encoder 13 is externally fitted and fixed to the portion deviating from the inner ring raceway 8b to the axially inboard direction in the axially inboard end of the outer peripheral surface of the inner ring 7. This encoder 13 is formed by combining a metal insert 14 formed on a generally annular shape having substantially an L-shaped cross section by a magnetic metal plate, and an encoder body 16 attached to a side surface of a circular ring part 15 constructing this metal insert 14. This encoder body 16 is formed in a generally circular ring shape by a permanent magnet such as a rubber magnet in which ferrite powder is mixed, and is magnetized in the axial direction and also the direction of magnetization is changed alternately at equal distances with respect to a circumferential direction. Consequently, south poles and north poles are arranged alternately at equal distances in the axially inboard surface which is a detected surface of the encoder body 16.
Also, a seal ring 17 is installed between the opening of the axially outboard end of the outer ring 2 and the outer peripheral surface of the axially intermediate portion of the hub body 6 and also, a cap 19 is attached to an opening of the axially inboard end of the outer ring 2. Accordingly, openings of both of the axial ends of space 18 in which each of the rolling elements 12, 12 and the encoder 13 are installed are closed to prevent grease packed into this space 18 from leaking to external space, or prevent foreign matter present in the external space from entering this space 18.
The cap 19 includes a bottomed cylindrical cap body 20 formed by injection molding of a synthetic resin, and a fitting ring 21 formed in a generally annular shape having an L-shaped cross section by stamping of a non-magnetic metal plate. The cap body 20 in this cap 19 includes a cylindrical part 22, and a bottom part 23 for closing an opening of the axially inboard end of this cylindrical part 22. The fitting ring 21 is fixed (molded) to the inner side portion of the distal end of the cylindrical part 22 in this cap body 20. Also, the portion near to the radially outside of the bottom part 23 is provided with a mounting part 24 (with an increased axial thickness dimension) bulged to the axially inboard as compared with the other portion. The portion axially opposed to the detected surface of the encoder 13 (encoder body 16) in this mounting part 24 is formed with a through hole 25 pierced in the axial direction. And, a bottomed cylindrical sensor insertion case 26 made of a non-magnetic stainless steel plate is internally fitted to this through hole 25. This sensor insertion case 26 is embedded in the mounting part 24 by insert molding at the time of injection molding of the cap body 20. Further, a nut 27 with a female screw formed on an inner peripheral surface is embedded in the portion deviating from the through hole 25 in this mounting part 24 by insert molding too.
A sensor unit 28 for detecting a rotating speed is supported and fixed to the cap 19. This sensor unit 28 includes a sensor 29 and a sensor holder 30. The sensor 29 in this sensor unit 28 is means for providing a detecting part with a magnetic detecting element such as a Hall element or a magnetic resistance element, and changes an output signal according to a change in characteristics of the detected surface of the encoder 13. The sensor holder 30 is formed by injection molding dieing of a synthetic resin, and includes an insertion part 31 for holding the sensor 29, and a mounting flange part 32 for fixing to the cap 19. Such a sensor unit 28 is fixed to the cap 19 (mounting part 24) by screwing a male screw part of a bolt 34 inserted into a through hole formed in the mounting flange part 32 into the female screw part of the nut 27 with the insertion part 31 inserted into the sensor insertion case 26.
According to the rolling bearing unit 1 with the rotating speed detector of the conventional structure having the above configuration, the wheel fixed to the hub 3 can be supported rotatably with respect to the suspension for supporting the outer ring 2. Also, when the encoder 13 is rotated together with the hub 3 with rotation of the wheel, south poles and north poles present in the detected surface of this encoder 13 alternately pass through the vicinity of the detecting part of the sensor 29 opposed to the detected surface of this encoder 13 through a bottom plate part 35 of the sensor insertion case 26. As a result, a direction of magnetic flux flowing in the magnetic detecting element constructing the sensor 29 is alternately changed and characteristics of this magnetic detecting element are alternately changed. Since a frequency at which the characteristics of the magnetic detecting element are changed in this manner is proportional to a rotating speed of the hub 3, the ABS or the TCS can properly be controlled by sending an output signal of the sensor 29 to a controller (not shown). Also, in the case of the conventional structure, the space 18 in which the encoder 13 is installed can be hermetically closed by the cap 19 (and the sensor insertion case 26) even in a state before the sensor unit 28 is assembled on an assembly line of an automobile manufacturer etc., with the result that foreign matter can effectively be prevented from adhering to this encoder 13.
However, in the case of the conventional structure as described above, the following problem may happen.
That is, in the case of the conventional structure, for example, a set of an upper molding die 36 and a lower molding die 37 as shown in FIG. 7 is used to manufacture the cap 19. Concretely, a melted synthetic resin is injected into a cavity 38 having a shape according to an outer surface shape of the cap 19 defined with the upper molding die 36 and the lower molding die 37 abutted in the axial direction. Particularly in the case of the conventional structure, the synthetic resin is injected into this cavity 38 with the sensor insertion case 26 set (insert molding is performed). Also, in order to set an installation position of the sensor insertion case 26 in the case of performing such insert molding, the bottom plate part 35 constructing this sensor insertion case 26 is abutted on a part of the lower molding die 37 and also, a part of the upper molding die 36 is abutted (bitten) on an axially inside surface (a convex curved surface) of a bent part 41 which is the part of continuity between a cylindrical part 39 and a rib part 40 constructing the sensor insertion case 26 similarly. Consequently, position accuracy of the bottom plate part 35 of the sensor insertion case 26 with respect to all abutting surface 42 (see FIG. 6) abutted on an axially inboard end face of the outer ring 2 in an assembly state in the cap 19 is controlled by dimension accuracy of the lower molding die 37, and position accuracy of the bent part 41 (abutting part) with respect to an axially inboard surface of the bottom part 23 constructing the cap 19 is controlled by dimension accuracy of the upper molding die 36.
Here, the sensor insertion case 26 is formed by stamping (deep-drawing) a non-magnetic stainless steel plate, and this non-magnetic stainless steel plate has high work-hardening properties, with the result that it is difficult to obtain high dimension accuracy (shape accuracy) stably by the deep drawing. Further, it is difficult to accurately regulate a shape (convex curved surface shape) of the folded part 41 in the sensor insertion case 26. As a result, an individual difference may be caused in a distance X from an axially outboard surface of the bottom plate part 35 of the sensor insertion case 26 to the portion, on which a part of the upper molding die 36 is abutted, in the bent part 41, and the following problem may be caused.
First, when the distance X is shorter than a distance Y defined by the upper molding die 36 and the lower molding die 37 (X<Y), a stamping force (bite amount) of the upper molding die 36 on the bent part 41 becomes inadequate, and a melted resin may leak out of this abutting portion to the inside of the sensor insertion case 26 and it may be solidified. In such a case, work of removing the solidified synthetic resin (burr) becomes complicated due to the fact that a bore diameter dimension of the through hole 25 is small.
On the other hand, when the distance X is longer than the distance Y (X>Y), wear (including scratch etc.) may occur in the portion abutted on the bent part 41 in the upper molding die 36, and the wear becomes a cause of a decrease in a life of the upper molding die 36. Also, deformation including buckling may be caused in the cylindrical part 39 constructing the sensor insertion case 26, and it may become resistant to inserting the insertion part 31 constructing the sensor holder 30 into the inside of this cylindrical part 39. Further, when injection molding is performed with the cylindrical part 39 elastically deformed (expanded) to the radial outside based on the pressing force of the upper molding die 36 and then the cap 19 is taken out of the cavity 38 (the pressing force by the upper molding die 36 is eliminated), the cylindrical part 39 is elastically restored (becomes small in diameter), with the result that a gap may be formed between an outer peripheral surface of the cylindrical part 39 and the portion present in the periphery of this cylindrical part 39 in the synthetic resin. Such a gap is not desirable since a decrease in sealing properties by the cap 19 is caused.
In addition, it is generally known that the synthetic resin is contracted by a decrease in volume in the case of being cooled and solidified. As a result, the gap formed by the cause as described above may be cleared or decreased by contracting the portion present in the periphery of the cylindrical part 39 in the synthetic resin constructing the cap body 20. However, it is difficult to completely clear the gap since a bore diameter dimension of the through hole 25 is normally about 10 mm and is small in diameter and the amount of contraction associated with solidification is small.
In the case of the conventional structure as described above, a problem of the need for work of removing the solidified synthetic resin from the inside of the sensor insertion case 26 or a decrease in sealing properties by the cap 19 or deformation of the sensor insertion case 26 may arise due to variations in dimension accuracy of the sensor insertion case 26.